This invention relates to catalysts and in particular to catalysts, or precursors thereto, containing an inert support material and at least one oxide of a metal of Group VIII of the Periodic Table and selected from nickel and cobalt.
For some catalytic applications the Group VIII metal oxide is the catalytically active species while for other catalytic applications the Group VIII metal oxide is a catalyst precursor and the catalytically active species is the product of reducing the Group VIII metal oxide to the Group VIII metal or is the product of oxidising the Group VIII metal oxide in the precursor to a higher oxidation state. For example catalysts obtained by reduction of a precursor containing nickel and/or cobalt oxide are of use as hydrogenation catalysts, eg methanation catalysts for the hydrogenation of carbon oxides to methane or catalysts for the hydrogenation of aromatic compounds such as benzene to cyclohexane. Another use of supported nickel and/or cobalt oxides is as catalysts for the decomposition of oxidising agents such as hypochlorite ions in aqueous solutions, for example in the treatment of effluents containing such ions prior to discharge of into rivers, lakes, or estuaries.
Aqueous media containing oxidising agents often have a relatively high pH: in order to prevent the catalyst particles disintegrating during use as a result of such alkaline conditions, it has previously been proposed to employ Group VIII metal oxides in intimate mixture with a metal oxide such as magnesia or alumina as a coating on a non-porous, hard fired, support of eg alumina or magnesia (see U.S. Pat. No. 4,732,688 and EP 276044) or to employ a resin binder, for example polyvinylidene fluoride, (see U.S. Pat. No. 4,400,304 and the reissue thereof U.S. Pat. No. Re. 32392). Catalysts made using the aforesaid inert non-porous supports have a relatively small Group VIII metal oxide content, typically less than 10% by weight, and usually less than 5%. While the initial activity of such materials is good, the service life of such catalysts is in some cases inadequate, as a result of loss of active material through loss of adhesion of the coating to the support. While particles made using a resin binder as aforesaid may have a somewhat greater Group VIII metal oxide content, the binder tends to restrict access of the effluent being treated to the active catalyst and also the binders necessary to withstand highly alkaline conditions are relatively expensive.